Introduction This page contains a general
overview of the functionality of VGA and SVGA cards into various sections,
and gives a description of the functions of each section. This is
intended to be a general description for those unfamiliar to the functionality
and capabilities of graphics hardware. The basic function of graphics
hardware is to allow the CPU to manipulate memory specific to the graphics
hardware, and to take the information stored in that memory and output
it in a form that a monitor or LCD panel can use.

Frame Buffer This is the component of
the video hardware that stores the pixels and information to be displayed
on the monitor. This is the center of the video hardware, as nearly
all operations are performed on or using this data. The frame buffer
is a form of RAM, which is typically located outside the main graphics
chip and are implemented using DRAM chips; however, more sophisticated
forms of RAM that are ideal for video hardware applications, such as VRAM.
The amount of video memory that is present determines the maximum resolution
that the hardware can generate. The frame buffer is usually mapped
into a region of the host CPU's address space allowing it to be accessed
as if it were a portion of the main memory. For example, in the VGA,
this memory is mapped into the lower 1M of the CPU address space, allowing
it to be directly accessable to real mode applications, which cannot directly
access the remaining memory. In the VGA, this memory is broken up
into 4 separate color planes, which are recombined to produce the actual
pixel values at the time of display generation.

Graphics Controller This is the video chipset's
host interface to the frame buffer, and is part of the main graphics chip
or chips. It allows the host CPU to manipulate the frame buffer in
a fashion suited to the task of graphics operations. It allows certain
methods of access that are designed to reduced the CPU requirements for
performing standard video operations, particularly in accelerated chipsets,
which can have a quite complicated set of access methods which can include
line drawing, area and pattern fill, color conversion/expansion, and even
3d rendering acceleration. For example, in the VGA the graphics controller
allows one write by the CPU to its mapped memory region below 1M to affect
all four color planes, as well as allowing faster transfers of video data
from one region to another in video memory.

Display Generation This portion of the graphics
hardware is involved in taking the data in the frame buffer, converting
the pixel or character information stored by the graphics controller, and
converting it into the analog signals required by the monitor or lcd display.
The pixel data is first sequenced, or read serially from the frame buffer,
then converted into analog color information, either by a palette look-up
table, or by directly converting into red, green, and blue components.
The CRT controller at the same time adds timing signals that allow the
monitor to display the analog color information on the display. For
example, in the VGA these components are made up of the sequencer, attribute
controller, CRT controller, DAC, and palette table. The sequencer
reads the information from the frame buffer, and converts it into pixel
color information, as well as sends signals to the CRT controller such
that it can provide the timing signals the monitor requires. This
color information is formatted by the attribute controller in such a way
that the pixel values can be submitted to the DAC. The DAC then looks
up these values in its palette table which contains red, green, and blue
intensities for each of the colors that the attribute controller generates,
then converts it into an analog signal that is output to the VGA connector
along with the timing signals generated by the CRT controller. If
the display is an LCD panel such as found in laptops, the DAC and associated
support hardware convert the pixel values to signals that the LCD panel
displays directly.